Dissolving of polymers



July Z3, 1946. R. c. HoUTz DISSOLVING OF POLYMERS Filed Nov. 4, 1944 fa?6% Wj ATmR EY Patented July 23, 1946 `UNITED STATES PATENT OFFICEDISSOLVING F POLYMRS Ray Clyde Houtz, Snyder, N. Y., asslgnor toE. I. duPont de Nemours & Company, Wilmington, Del., a corporation of DelawareApplication November 4, 1944, Serial No. 562,016

(Cl. 26o-32) 1 13 Claims.

'I'his invention relates to a new composition of matter and shapedarticles produced therefrom. More particularly, this invention relatesto an organic solvent solution of polyacrylonitrile, i. e. polymerizedacrylonitrile or polymerized vinyl cyanide (CH2=CHCN)I, and copolymersand interpolymers of acrylonitrile in which at least 85% by Weight ofthe polymer is acrylonitrile, and to the production of shaped articlesfrom said organic solvent solution of said polymers of acrylonitrile.

Polyacrylonitrile, and copolymers and interpolymers of acrylonitrilewith other polymerizable substances, for example vinyl or acryliccompounds, in which at least 85% by weight of the polymer isacrylonitrile have been known for some time and recognized as possessingdesirable physical and chemical properties including toughness andnsolublity in and insensitivity to common organic solvents such asmethyl or ethyl alcohol, acetone, ethyl ether, ethyl acetate,hydrocarbon solvents, chlorinated hydrocarbons and the like. Because ofthese facts, numerous attempts have been made to form these polymericmaterials into yarns, films and other shaped articles.

The copending application of George H. Latham, Serial No. 562,012, ledof even date herewith discloses solutions of polyacrylonitrile indimethyl carbamy1 compounds and the production of extruded and otherwiseshaped articles and structures from such solutions. The abovesaidapplication of George H. Latham represents the first successfuldissolution of polyacrylonitrile in a solvent to produce a solutionwhich is suitable for the production of commercially useful textileyarns or wrapping tissue films and similar tough, iiexible structures.

The present application relates to a similarly satisfactory dissolutionof polyacrylonitrile in an organic solvent taken from a different classof organic compounds and the polyacrylonitrile solutions producedthereby are similarly satisfactory for the production of tough,iiexible, dense, colorless yarns and lms which are suitable for use inpractically all general commercial applications of such products.

It has been known heretofore that concentrated aqueous solutions ofinorganic salts such as lithium bromide, zinc chloride and sodiumsulfocyanide will dissolve polyacrylonitrile and it has been proposed(Rein U. S. Patent No. 2,140,921) to employ the resulting solutions inthe formation of yarns and illms. However, it has been foundsubstantially impossible to use the resulting compositions in such amanner. Their extrusion into coagulating baths o! the type proposed(including such non-solvents for acrylonitrile as water, dilute acid,dilute salt solutions, etc.) result in the formation of shaped articlesthat contain large amounts of the inorganic salt of the proposedsolvent. These salts are distributed throughout the structure anddestroy the continuity of the polyacrylonitrile phase and the structurepossesses poor` physical properties. Removal of these salts, whenpossible, results in the formation of a porous, spongy, weak,undesirable structure that is very brittle and completely unsuited foruse as a yarn or film. Moreover, when it is attempted to form amultiillament yarn by extruding, for example the proposed aqueous sodiumsulccyanide pclyacrylonitrile composition, into a dilute acid bath, itis found that the individual laments obtained stick together to form anessentially monolament structure that is extremely brittle and cannot bebent or Worked without breaking.

U. S. Patent No. 2,167,537 to Tobis points out that certain copolymersof acrylonitrile and an acrylic acid ester (those copolymers containingnot more than of acrylonitrile) are soluble in mixtures of organicsolvents such Las dioxan, monochlorbenzene, cyclohexanone, etc. However,these liquids are incapable of dissolving or even swellingpolyacrylonitrile or copolymers of acrylonitrile containing higherpercentages of acrylonitrile, i. e. acrylonitrile polymers of the typewith which this invention is concerned. As previously mentioned,polymers containing such high percentages (at least by weight) ofacrylonitrile are especially desirable for use because of their goodphysical properties and excellent chemical resistance.

It has also been proposed (Rein U. S. Patent No. 2,117,210) to dissolvepolyacrylonitrile in molten Quaternary ammonium salts such as benzylpyridinium chloride, an ionizable salt. Although the resulting solutioncan allegedly be used to form yarns or films of polyacrylonitrile, thesolution itself is dark red to brown in color, indicating that somedecomposition of the polyacrylonitrile or some reaction between thepolyacrylonitrile and the molten salt has probably taken place. Suchsolutions are not satisfactory for the production of commerciallyuseful, shaped `articles of polyacrylonitrile. Here again, it has beenfound practically impossible to obtain lamentary structures such asyarns from the composition. Films or filaments, when obtainable', areextremely brittle; they are highlycolorecl-l and very weak, presumablybecause oi the presence within them of residual quaternary ammoniumsalt. Removal of this salt is dimcult and the resulting structurescontain numerous and large voidsthat make the structures substantiallyuseless for commercial purposes.

It is therefore an object of this invention to dissolvepolyacrylonitrile or a copolymer or interpolymer of acrylonitrile inwhich at least 85% by weight of thepolymer is acrylonitrile, in'asolvent which does not react with or decompose the polymer and which maybe substantially completely removed from the structures formed oi' sucha solution.l

It is another object of this invention to produce a solution ofpolyacrylonitrile or a copolymer or interpolymer of acrylonitrile inwhich at least 85% by weight of thepolymer is acryloni' trile, in asolvent which does not react with or decompose the polymer, the solutionbeing suitable for the formation of commercially. useful, void freearticles of polyacrylonitrile, for example yarns which are suitable astextile yarns and films which are suitable as wrapping tissue.

It is another object of this invention to produce a solution ofpolyacrylonitrile, or a copolymer or asoqns strong hydrogen-bondingforces and in order to dissolve one o! these polymers, it is necessaryto iind a material which will undergo hydrogenbonding with the activehydrogen bonding groups of the polymer molecules and thus weaken thestrong hydrogen bond within the polymer molecule and cause the hydrogenbonding forces to be shared between molecules of the polymer and thesolvent. In this manner. it is possible to form interpolymer ofacrylonitrile in which at least 85% by weight of the polymer -isacrylonitrile, in a volatile organi-1 solvent. which solution is stableover extended periods of time and is eminently suited for use in themanufacture of shaped articles srch as yarns, lms, tubes. straws,artificial horsehair, bristles and ribbons. or when highly concentrated,for use in the manufacture of molded articles.

It is a still further object of this invention to produce shapedarticles and structures of polyacrylonitrile, or'copolymers orinterpolymers of acrylonitrile in which at least 85% by weight of thepolymer is acrylonitrile.

It is still another object of this invention to produce a shap=d articleor structure oi polyacrylonitrile or copolymers or interpolymers ofacrylonitrile in which at least 85% by weight of the polymer isacrylonitrile, for example a yarn, film, tube, bristle or the like whichis tough, ilexible, tenacious and free from voids. I

Other objects of the invention will appear hereinafter.

The objects of the invention may be accomplished in general bydissolving polyacrylonitrile, or a copolymer or interpolymer ofacrylonitrile in which at least 85% by weight of the polymer isacrylonitrile in an organic compound containing a thiocyanometnyleneCHSCN) group and which is not a salt.

Ii the solvent has a relatively low boiling point (less than about 250C.), the solution of acrylonitrile polymer may then be formed into ashaped structure, for example a yarn or film, and the solvent removedfrom the shaped structure to coagulate the same. When the solvent isrelatively non-volatile and has a boiling point of about 300 C. or more,shaped articles may bemade from the solution and at least a portion o1'the solvent may be retained therein as a plasticizer for the articles.

It has been recognized in recent years that under certain conditions, anatom of hydrogen is attracted by rather strong forces to twn atomsinstead oi' only one so that it may be considered to be acting as a bondbetween them. This is called the hydrogen bond.

The diillculty of dissolving polymers containing at least 85% by weightof acrylonitrile is due to the presence within the polymer molecules ofa molecular dispersion of the polymer within the solvent and thus form asolution.

However. the strength oi.' the hydrogen bonding capacity cannot be takenas the sole criterion as to whether or not a compound will function tcdissolve an acrylonitrile polymer. It is also necessary that, in orderto function as a solvent for an acrylonitrile polymer, the coinpoundcontain certain ble of satisfactorily sharing a hydrogen bonding forcewith the particular active group of the acrylonitrile polymer. Inmost-instances, these .groups require the presence of a hydrogen atom ona carbon atom to which the group is attached (designated asalpha-hydrogen atom). Such groups as require the alpha-hydrogen atom areineffective to impart solvent power if the alphahydrogen atom lsmissing.

It has now been found that groups capable of conferring solvent powerinclude dimethyl carbamyl CM- [Ca Iormyl imido atom within their ownstructures.) i Thus, the groups dimethyl carbamyl CHI 0 C: formyl imido(HCON cyanomethylene CHCN), thiocyanomethylene CHSCN) andsulfoxymethylene CHSO, CHSOO, and CHSO2O-) shall hereinafter be referredto as solvogenic groups and compounds containing them are frequentlycapable of dissolving an acrylonitrile polymer containing at least byweight of acrylonitrile.

In the event that two or more groups requiring the presence of analpha-hydrogen atom in order to render them solvogenic are attached tothe same carbon atom and compete with each otherffor an availablealpha-hydrogen atom, the sulfoxy group, the cyano group and thethiocyano group take preference over each other in the groups which willbe capaorder named, to form the solvogenio group, the lower rankinggroup or groups present assuming merely the nature of an inertsubstituent on the carbon atom.

It has furthermore been found that compounds containing theabove-mentioned solvogenic groups will be solvents for theabove-mentioned polymers only if the carbon content of the compound bewithin certain limits as given below. If the ratio of carbon tosolvogenlc groupings is maintained within the said limits, the compoundswill retain solvent properties of the polymer even though the moleculebe of considerable size and complexity. The solvent power of thecompound for acrylonitrile polymers is increased if additionalsolvogenic groups are present in the molecular structure of thecompound, the eect of these groups being additive.

'It has now been found, in accordance with this invention. that organicthiocyanomethylene compounds which are fusible without decomposition andparticularly those thiocyanomethylene compounds embraced by thefollowing empirical formula, and preferably having a melting point below250 C., will dissolve polyacrylonitrile, and copolymers andinterpolymers of acrylonitrile in which at least 85% by weight of thepolymer is acrylonitrile:

wherein m and q are integers equal to or greater than zero; u is aninteger equal to or `greater than 2, except that when the sum m-l-q isgreater than zero, u may equal 1; n, p and r are integers of such valuethat n/m is equal to or less than 1.5; p/q is equal to or less than 1.5and r/u is equal to or less than 0.5.

These compounds are not salts but may be cyclic or acyclc in nature andmay possess one or more ethylenic or acetylenic linkages. Valences otherthan those contained in carbon-to-carbon linkages and not shown assatlsiied by the above formula must be satisfied by hydrogen, oxygen,bivalent sulfur, halogen, hydroxyl, thiol, cyano or thiocyano or sulfoxygroups, the total number of halogen, oxygen, sulfur, hydroxyl and thiolsubstituents not exceeding one half the sum m-i-q-l-,u and the totalnumber of such non-solvogenic cyano. thiocyano and sulfoxy substituentsnot exceeding the sum m+q+u. The respective tolerances for the saidgroups oi substituents are independent of each other and members of eachgroup may be present in the molecule up to their group tolerances. Theoxygen or sulfur atoms may appear in the compound as bivalent groupseither as a side group (carbonyl or thiocarbonyl) or within the chain(ether or thioether) as the case may be. It is preferred that the carbonatoms in the Cn, Cp and Cr portions of the above formula be joined toeach other, but this is not essential.

Representative compounds coming within the scope of the above formulaand suitable for use as solvents for the above-mentioned acrylonitrilepolymers include:

SCN S CN Hz C H C Ha O H 2,3 dithiocyauo-l-propanol N C S-C H= C HS C N1,2 dithiocyanoetliylene BCN NCB-CHCHCHaSCN 1,2,3 trlthlooyanopropanoCHiCHCHnBCN CN 1,2 dlthiocyanopropane 8 CN 8 CN NCS-CHaH-CHCHaSCNl,2,3,4 tetrathlocyanobutmo B CN V l Nos-onion'omoms'cz 1.2,4 mmymbuuneBr NCS-CHIJJHSCN Lumina-1,2 damdcymrnme (Noscnmo Bixbiocyanomethynether(Nos-onine rBis(tliiocyanouiethyl) lnlndo NC8-CH=CCH|BCN 1,2,3uithlocyanopropene NCBCH|CH|CH|CN Gammmthiocyanobutyronltrlle CH:NCB-CHICHCN Beta-thiocyanolsobntyronltrlle CN NCB--CHICHCHICHgSCN2cyanol,4dithiocyanobutane C NC N NCS-CHrHCHCHzSCN2,3dicyano-l,4ditliiocyanobutane CN clcmenonlscN zeys'ni-'zniocynofm cNsCN C Hs H H C Hx 2-cyano-3-thiocyanobutano C HIC H C Hz C N CNBeta-thiocyanobutyronitrile NCS-CHICHCHICN HBetshydroxy-gammathloeyanobutyronitrile OH N C S-C Ha H Cv.lllplia-hydroxybeta-thlocyano-propionitrila NcscHicHloNBeta-thlocyanoproplonitrlle Nos-cmo oNHm N,NdlmethyltliiocyanoacetamidoCHICHC ON(CHI)1 N.N-dlmethyl-alglg-thiocyano-propionamideNCS-CHzCHsCONwHx): N,Ndlmethyl-beta-thlocyanopropionamide NCS-CHICIhCEC0N(CHa)n N,Ndinietbyl-alpha-cyanogamma-thiocyanobutyumideNCB-CHxCHrCHsCHICON(CHs)r]s NCB-CHsCHsCBsC N(CHs)sN,Ndimsthylgammsthiocysnobutynmids NCB-CHIOHICHICHICNDolto-thiocysnovaleronitrilo NCSCHsCH(CN)s (Thioeysnomethyl)mslononitrile C Hs CHaCHiHCHaSCN lZ-cyimo-l-thiocysnobutaneAcrylonitrile polymer solutions formed by the use oi' solvents embracedby the formula set forth above are stable at room temperature(approximately 20 C.) and at temperatures considerably above roomtemperature. Shaped structures and articles can be produced by extrudingmany of such solutions into an evaporative or coagulative medium. Byforming the structures in an evaporative medium. the solvent must beevaporated therefrom and by forming the structures in a coagulativemedium, the solvent should be removed by selective solution in anon-solvent for the polymer.

The solutions are prepared by dissolving the polyacrylonitrile, orcopolymer or interpolymer of acrylonitrile with one or a mixture of theabove-mentioned solvents. SomeV of these solvents are solid at ordinarytemperatures and dissolve or retain the polymer in clear solution onlyat elevated temperatures, for example at temperatures of 100 C. orhigher. below which temof the above class, the resulting compositionwhile hot has the appearance of a true solution. When cooled to roomtemperature, the composition generally takes on the appearance of a gel,which gel may, on standing, undergo syneresis. AIi'teheating of this gelor syneresed mass however causes it to again return to solution form.

In view of the relatively high melting points of some of the solvents ofthis invention, they would have comparatively little use in theproduction of a polyacrylonitrile spinning or casting solution. Suchsolvents are however excellent solvent plasticizers forpolyacrylonitrile since they are soluble in a wide range of proportionswith the said acrylonitrile polymers. The presentV invention thereforecontemplates solid solutions of acrylonitrile polymers containing atleast by weight of acryionitrile as well as liquid solutions thereof.

Shaped articles obtained from solvent solutions of polyacrylonitrile inaccordance with the invention and from which the solvent is subsequentlyremoved are substantially free of foreign matter and voids andsubstantially undecom posed and chemically unchanged from the simplepolymer prior to its solution.

The`above-described organic solvent solutions of acrylonitrile polymermay be shaped in the form of filaments, yarns, films, tubes and likestructures by apparatus and processes generally known in the art, thedetailed operating conditions being suitably modified.

Suitable methods and apparatus for the production of shaped articles ofthe polymers of this invention will be readily apparent by reference tothe following detailed description when vtaken in connection with theaccompanying illustrations in which:

Figure 1 is a diagrammatic vertical sectional view showing a dryspinning cell suitable for use in accordance with the invention;

Figure 2 is a diagrammatic perspectivev view showing a yarn drawingdevice for use in connection with the invention; l

Figure 3 is a diagrammatic perspective view showing a wetspinning-apparatus for use in the invention; and

Figure 4 is a diagrammatic side elevational view showing a suitable filmcasting apparatus for use in accordance with the invention.

Referring to Figure 1 of the drawing, reference numeral il designates aspinneret through which a plurality of filaments I5 are formed byextruding a ilament-forming solution supplied to the spinneret by meansof conduit I3. The spinning cell is jacketed with a material i1 such asa refractory in which is embedded an electrical heating coil i9. Thespinning cell can thus be operated at any desired temperature. Aplurality of conduits 2| are provided adjacent the bottom of the devicefor passing evaporative medium through the cell so as to evaporate thesolvent from the extruded filaments I5. The evaporative medium isremoved vfrom the cell through outlet openings 23. The yarn comprisingthe plurality of filaments |5'is passed from the bottom of the spinningcell around guide roller 25 and is wound on a bobbin 21.

' Referring to Figure 2 of the drawing, the yarn i5 is removed from thebobbin paokage 21' and passed about draw roller 29, and separatingroller 3|. From draw roller 29, the yarn is passed to a second drawroller 33 and separating roller 35. The yarn is passed around the twosets of draw rollers including their separating rollers a sufficientnumber of turns to prevent slippage of the yarn. Draw roller 33 isrotated at a greater speed, for example three toten times the speed ofdraw roller 29. In this manner, the yarn I is stretched between the twodraw rollers. "AS the yarn passes between the two draw rollers, aheating medium is brought into contact with the yarn througi blowernozzles 31 and 39. The yarn passing from the draw roller 33 is wound onbobbin 4I. The drawing or stretching of the spun yarn as described isnot claimed as part of the present invention, but is claimed in thecopending application of Daniel T. Meloon, Serial VNo. 496 397, filedJuly 28, 1943.

Figure 3 of the drawing illustrates a wet spinning apparatus for theproduction of yarn. The acrylonitrile polymer solution is passed throughconduit 5| and is extruded through spinneret 53 to form a multilamentyarn 54. The yarn. 54 is passed about guide roller 51 which ispositioned within the coagulating liquid in tank 55. The yarn is thenpassed about guide roller 59 and is wound on bobbin 6l.

The organic solvent solution of polyacrylonitrile may be cast inthe formof a film as illustrated in Figure 4. In accordance with this apparatus.the polymer solution is passed from hopper `1| on to the endless steelband 13 where it is smoothed by means of a doctor knife 15. The band,together with the lm, is passedfunder a means 11 for bringing a heateddrying medium into contact with the film. The film 8| is pulled from theband 13 and collected on a mill roll 83.

The polyacrylonitrile for use`with the invention is preferably preparedby thev ammonium persulfate catalyzed polymerization of monomericacrylonitrile dissolved or emulsiiled` in water. It can, however, beprepared by any other suitable type of polymerization reaction such as,for example, the emulsion type reaction disclosed by U. S. Patent No.2,160,054 to Bauer et al. The polymer preferably possesses a molecularweight within the range of 15,000 to 250,000 or even higher, ascalculated from viscosity measurements by the Staudinger equation: i

N Molecular Weight- KMC and C=concentration of the solutionexpressed asthe number of moles of the monomer (calculated) per liter of solution.

The molecular weight of the polymer obtained is dependent on suchfactors as the concentration of the monomer in the water, the amount andtype of catalyst present, the temperature of the reaction, etc. Forexample, polyacrylonitrile, having a molecular weight of approximately60,000 can be prepared as follows: To 94 pounds of distilled waterheated to 40 C. add 40 grams with the principles of this invention andof l taining at least 85% by weight of acrylonitrile and likewisepreferably having a molecular weight of 15.000 to 250.000 or higher canbe` prepared in a similar manner.

'I'he following examples illustrate preferred methods of preparingsolutions in accordance employing these solutions inthe manufacture ofcommercially satisfactory shaped articles. The invention is not to belimited by the details set forth in the examples.

Example I Fifteen (15) parts of an acrylonitrile polymer f 'viscositydata are ground to an average particle c size of 100 mesh and mixed with85 parts of finely of ammonium persulfate catalyst and 80 grams ofsodium bisulte activator. pounds of acrylonitrile slowly with stirringover a period of two hours. having the above said molecular weight willprecipitate from the solution. Increasing or decreasing the amount ofthe catalyst, while maintaining the other conditions constant, decreasesor increases the molecular weight of the polymer.`

Acrylonitrile copolymers and interpolymers con- Then add 16` Thepolyacrylonitrile ground ethylene thiocyanate. the resulting mixturebeing heated within a period of twenty-five minutes to a temperature ofC. to form a clear solution. The solution is extruded at a temperatureof 115 C. into a bath comprising triethanolamine heated to a temperatureof 115 C. to form a 10-f1lament yarn having a total denier of 100. Abath travel of 30 inches is employed, the yarn being subjected to atension of 0.4 gram per denier during its travel through the bath. Theyarn which possesses a tenacity of 3.0 grams per denier and anelongation of 12% is lustrous in appearance. It is substantially free ofvoids.

Example II Seventy-five (75) parts of the copolymer prepared by thecopolymerization of 98 parts of acrylonitrile and 2 parts ofN-dimethylaminoethyl methacrylate (acrylonitrile content of 95.1%) andpossessing an average molecular weight of 100,000 as determined by theStaudinger equation from viscosity data are ground to an average`particle size of 200 mesh and mixed with25 parts of trimethylenethiocyanate. The resulting mixture is molded at a temperature of C. toform a strong, rod-like structure.

As indicated in the above examples, it is possible by the practice ofthis invention to obtain a solution of polyacrylonitrile, or a copolymeror interpolymer of acrylonitrile which is eminently suited for use inthe manufacture of shaped articles such as yarns, films, or moldedarticles. These 'solutions are also suited for use as lacquers orcoating compositions. They are especially useful in the coating of wireand electrica-l parts where the high chemical and electrical resistanceof the polymer is important.

For the purposeof definition, a solvent is a material which, when in theliquid state, is capable of forming solutions in which the polymer ispresent in a concentration by weight of 5% or more. In most instances,the polymer is soluble in almost all proportions although themiscibility may take place at elevated temperature-s in the case ofcertain compounds. y

As also shown` the solvents of the invention are useful not only inconnection with the polyacrylonitrile. but also` with copolymers andinterpolymers of acrylonitrile with other polymerizable substances suchas. for example, compounds containing one or more ethylenic linkagesincluding vinyl and acrylic compounds as well as olenic or dioleiinichydrocarbons, such as isobutylene. butadiene, etc. They are eminentlysatisfactory for data using the vention must be `yarn or other shapedarticle use with thosepolymers that contain an appreciable amount ofacrylonitrile, for example polymers. copolymers and interpolymers thatcontain at least 85% by weight of acrylonitrile and that have generallybeen regarded by the art as being completely insoluble in all commonorganic solvents. Nor are these solvents limited to use with apolyacrylonitrile of `any given'molecular weight. They can be used witha polymer-of a1- most any given molecular weight, and are especiallysatisfactory 'for use with those polymers having an average molecularweight within the -range 15.000 to 250,000 as determined by viscosityStaudinger equation and intended for use in the manufacture .of yarns orfilms.

'I'he solution of acrylonitrile polymer dissolved in an organic solventin accordance with this inof such a concentration that its viscosity atthe operating'temperature is within a workable range. When it is to beemployed in yarn or the casting of film, the preferably have a viscositywithin the range of 25 to 750 poises. When the polymer has a molecularweight of 250,000 or more, this requires that the maximum concentrationof polymer in the spinning solution be of the order of Generally, it ispreferred that the spinning solution contain at least 10% of the polymerbecause oi' the dimculty of rapidly re'- moving large amounts of solventfrom the solution in the spinning operation. Moreover, it iseconomically undesirable to use such large amounts of solvent for thespinning of a given amount of polymer although it is true that thesolvent can be completely recovered from the spinning operation andreused. For these reasons, it is'preferred to employ a polymerA havingan average molecular weight of between 40.000 and 150.000 since such apolymer forms a solution of the desired viscosity in concentrations ofthe order of to 25%. and at a desirable spinning temperature of theorder of 100 to 150 C. Of course. it is within the scope of theinvention to heat the solution to a higher temperature. even to abovethe normal boiling point of the solvent.

viscosity of the solution.

The evaporative spinning of filaments and yarns ing o f films inaccordance with this invention may be any vapor inert to the fllmornlament-forming solution such as air, nitrogen. steam, etc., or anysuitable mixture thereof. The temperature of the evaporative medium isdependent on such factors -as the dimensions of the spinning cell, thecomposition and rate of extrusion o1' the sp'nning solution and the rateof flow of the evaporative medium. It is only necessary that theseseveral factors be so correlated that the leaving the spinning or thedry castcally inert non-solvent for mer. As examples of such tionedwater, glycerin. alcohol, ether, etc., or

alkalies or acids. The

the acrylonitrile polya liquid may be menorganic solvents, such asaqueous solutions of salts. copending application 0f medium employed inthe dryA preferably at l2 'f William W. Watkins, Serial No. 498.376,illed July 28, 1943, covers the use of glycerol, triethanoltial tensionand stretch being applied during spinning.

The article of acrylonitrile tained polymer thus obcan advantageousLv besubjected to a the peripheral speeds "of that the article is stretchedto from two to ten times its original length. preferably approximatelysix times its original length. This stretching of the formed article maybe performed at any suitable time. However, in the case of articlesformed by the wet spinning or casting technique, it is preferablyperformed beforethe article 'I'his stretching of the shaped article canalso be accomplished by causing the article, while passing betweenstretching rollers, to contact a heated stationary pin, or to passthrough an inert medium such as air, water, glycerin, etc. heated to ahigh temperature. Obviously, the article must not be exposed to thishigh temperature for a period sufllciently long to decompose thepolymer. In general however, the time of contact of the article with theheated medium is so short that temperatures up to 250 C. canbe employed.Although it is generally preferred to heat the article to a temperatureof at least C. during the stretching operation, this is not essential.Desirable results can be obtained by stretching the article without theapplication of heat, for example by stretching at room temperature.

In addition to acting as solvents for acrylonitrile, or copolymers orinterpolymers of acrylonitrile, the thiocyanomethylene-containingcompounds of this invention, when present in small amounts, can also beused as plasticlzing agents for the polymer and the higher boilingcompounds of the invention are especially suited for such a lowerboiling solvent, for example to a solution s of the polymerin ethylenethiocyanate'.

`This invention is primarily concerned with the steps of dissolvingpolyacrylonitrile in a suitable solvent to form a stable solutionadapted for use provided by it are solvents do not cause a decompositionor chemical alteration of the dissolved acrylonitrile poiymer. At thesame time, it is also characteristic that stable; the

13 be incorporated in the acrylonitrile polymer solution to modify theproperties, both chemical and physical of the resulting shaped articles.

This invention provides a class of solvents for polyacrylonitrile, andcopolymers and interpolymers oi acrylonitrile which were heretoforeconsidered substantially insoluble. The solvents are capable of formingwith the polymer clear solutions that are stable for extended periods of`time at both room and elevated temperatures and are admirably suitedfor use as lacquers or coating compositions or in the manufacture ofshaped articles of the polymer, for example by extrusion into anevaporative or coagulative medium, or by the use of a molding technique.

The invention also provides a class oi materials that is eminentlyVsuited for use in plasticizing` structures comprising the acrylonitrilepolymers. The materials provided by this invention are apparently truesolvents for the above-mentionedv acrylonitrilepolymers. They do nottend to react with or decompose the polymer, the polymeric materialobtained from the solution of this invention apparently being of thesame identical chemical composition as the initial polymer.

Yarns, iilms and similar articles of polyacrylonitrile prepared from thesolutions of this invention can be stretched to yield orientedstructures that possess a high tenacity, a desirable elongation and ahigh elastic recovery that compares favorably with that of silk. Thearticles are not contaminated with undesirable salts and they aresubstantially free oi void spaces. l

Reference, throughout the specification and claims, to acrylonitrilepolymers, polymers of acrylonitrile, and copolymers and interpolyrnersof acrylonitrile containing at least 85% by weight of acrylonitrilesigniiies polymers containing in their molecules at least 85% by weightof the acrylonitrile unit which is considered to be present in thepolymer molecule as the group oHr-H-CN that is, at least 85% by weightof the reactant material converted into and forming the polymer isacrylonitrile.

Since it is obvious that many changes and' modications can be made inthe above described details without departing from the nature and spiritof the invention, it is to be understood that the invention is not to belimited to the details described herein except as set forth in theappended claims.

I claim:

1. As a new composition of matter, a polymer of acrylonitrile containingin the polymer molecule at least 85% by weight of acrylonitriledissolved in an organic thiccyanomethylene compound embraced by theformula:

wherein m and q are integers at least equal to zero; u. is an integer atleast equal to 2, except that when the sum mA-q is greater than zero, u

may equal 1; n.1: and r are integers of such value that n/m does notexceed 1.5; p/q does not exceed 1.5 and r/u does not exceed 0.5; allvalences of said compound other than those contained in carbon-to-carbonlinkages and not shown as satisned in the formula being satisfied by asubstituent taken from the group consisting of hydrogen, halogen,oxygen. bivalentl sulfur, hy-

droxyl, thiol, cyano, thiocyano and sulfoxy radicals; the total numberof halogen, oxygen, sulfur, hydroxyl and thiol substituents notexceeding one half the value of m+q+u, and the total number oi suchcyano, thiocyano and sulfoxy groups not exceeding the sum m-l-q-l-u.

2. A new composition of matter as denned in liaim i, in which thepolymer is polyacrylatrile.

, 3. A new composition o matter as denned in claim 1, in which thepolymer has a molecular weight of between 15,000 and 250,000.

4L A new composition of matter as dened in of acrylonitrile containingin the polymer molecule at least 85% by weight of acrylonitriledissolved in ethylene thiocyanate.

'7. As a new composition of matter, a polymer of acrylonitrilecontaining in the polymer molecule at least 85% by weight ofacrylonitrile dissolved in trimethylene thiocyanate.

8. As a new composition of matter, a polymer oi acrylonitrile containingin the polymer molecule at least 85% by weight of acrylonitrile and anorganic thiocyanomethylene compound embraced by the formula:

wherein m and q are integers at least equal to zero; u is an integer atleast equal to 2, except that when the sum m-l-q is greater than zero,vu may equal 1; n, p and r are integers of such value that n/m does notexceed 1.5: i/q does not exceed 1.5 and r/u does not exceed 0.5; allvalences of said compound other than those contained in carbon-to-carbonlinkages and not shown. as satised in the formula being satised by asubstituent taken from the group consisting of hydrogen, halogen,oxygen, bivalent sulfur, hydroxyl, thiol, cyano, thiocyano and sulfoxyradicals; the total number of halogen, oxygen, sulfur, hydroxyl andthiol substituents not exceeding one half the value of m+qlu, and thetotal number of such cyano, thiocyano and sulfoxy groups not exceedingthe sum m-l-q-l-u.

9. The composition of claim 1 in which the solution contains at least10% of said polymer of acrylonitrile.

l0. The composition of claim 1 in'which the polymer is polyacrylonitrilehaving a molecular weight of between 15,000 and 250,000.

11. The composition of claim 1 in which the polymer vispolyacrylonitrile having a molecular weight of between 40,000 and150,000.

12. The composition of claim 6 in which the polymer ispolyacrylonitrile.

13. The composition of claim 'l in which the polymer ispolyacrylonitrile.

RAY CLYDE HOUTZ.

" L,Potenr.No.2,401,713.

Qertillca'te ot Correction 7 RAY CLYDE HoU'rz It ishereby certified thaterrore appear in ther rinted specification of the above numbered patentrequiring oorrectlon as follows:v Cglumn 4line 37, for that portion ofthe form reading v une es, fera-s--Nwred (-S-C-N); linen, forthttportion of the formula i read -S-Q, read -.S-0, column 5,l lme 32,column 13, line 67 claim 1,

and co umn 14, hne 38, clalm 8, for the indistincteubscriptin thestructural formula,

right-handlpo ion thereof, before the closing bracket inA each instlnce, read u; column 12, line 5,l inning or read spinning o column 13,line 65, claim 1, in the formula, for the in read 8; and that the saidLetters Patent should be read with these corrections therein that thesame may conform to the record ofthe case in the lPatent Oilce.

Signed and sealed this 12th day of November, A. D. 1946.

LESLIE FRAzER, l

First Assistant Uommsoner of Patente.

July 2a, 194e.

lstinct subscript following CH inside the first closingparenthesis,

